Viscosity Index (ASTM D2270)

Single-number rating of how much viscosity changes with temperature; high VI oils (≥ 100) stay fluid at low temperature and film-protective at high temperature.

FuelViscosityLube

Loading calculator…

This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

VI = \frac{L - U}{L - H} \cdot 100

Symbol	Meaning	Unit
$L$	Low-VI reference 40 °C viscosity	cSt
$H$	High-VI reference 40 °C viscosity	cSt
$U$	Sample viscosity at 40 °C	cSt
$VI$	Viscosity index

Source: ASTM D2270

In short

Single-number rating of how much viscosity changes with temperature; high VI oils (\u2265 100) stay fluid at low temperature and film-protective at high temperature.

Learn the theory Bunker Quality and ISO 8217 Marine Fuel Standards